Telephone system



Patented Dec. 28, 1920.

3 SHEETS-SHEET l- W. T. POWELL.

TELEPHONE SYSTEM.

APPLICATION FILED MAR.29, 1918.

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TELEPHONE SYSTEM.

APPLICATION FILED MAR.29,1918.

W. T. POWELL.

TELEPHONE SYSTEM.

APPLICATION. FILED MAR. 29. 1918.

1,363,268. 7 Patented Dec. 28, 1920.

3 SHEETSSHEET 3.

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UNITED STATES PATENT OFFICE.

WINFRED T. POWELL. OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERNELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. 'Y., A CORPORATION OFNEW YORK.

TELEPHONE SYSTEM.

Specification of Letters Patent. Patented Dec; 28, 1920.

Application filed March 29, 1918. Serial No. 225,444.

T 0 all whom. it 111 ay con 0cm Be it known that I, mrnno T. POWELL,

a citizen of the United States, residing at East Orange, in the countyof Essex, State of New Jersey, have invented certain new and usefulImprovements in Telephone Systems, of which the following is a full,clear, concise. and exact description.

This invention relates generally to telephone exchange systems, and moreparticularly to such systems wherein telephone connections between thesubscribers lines are established and maintained by the agencyof'automatic switching mechanism operated in response to the act'ofinitiating a call, together with directively operable switchingmechanism actuated under the'control of the calling line and in responseto electrical impulses transmitted thereover.

Telephone exchange systems whether of the full automatic orsemi-automatic type may be briefly considered as consisting of twodistinct classes, so far as concerns the method in which the preliminaryswitching operations involved in the establishment of a connection areeffected automatically as a result of the usual act of removing thereceiver from the switchhook upon the initiation of a call. In systemsconstituting one of these classes. it is the practice to have thetelephone line of each subscriber to an exchange terminate in a line orindividual switch. These switches are arranged to have access to trunkcircuits leading to a plurality of selector switches and may becontrolled by automatic devices in such a manner that the individualswitch of each line when not in use is constantly maintained inoperative relation to a trunk which leads to an idle selectorswitch. hena subscriber, desiring to connect his line with the line of some othersubscriber. removes his receiver from the hook, the line switchindividual to his line. being thus prepositioned before an idle trunk,is instantaneously operated to connect his line directly through to afirst selector switch; The subscriber may then begin to transmitimpulses immediately after initiating the call with the assurance thatsuch impulses will be properly directed to the circuit extendingswitching mechanism. While systems involving the use of individualswitches possess the desirable feature of immediate connection to idletrunks, and the incident insurance against impulse mutilation, there isthis undesirable factor to be considered, that a comparatively largenumber of switches are required.

In another class of automatic switching systems, above alluded to, thesubscribers lines, instead of each being provided with an individualswitch, are terminated in the multiple contacts of line finder switches.These finder switches may be arranged to serve vany one of a largenumber of calling lines. \Vhen a subscriber initiates a call, acondition is placed upon his line such that a finder having accessthereto is set in operation to connect with the calling line and extendthe same to an idle selector switch. After the finder has completed itsfunction the calling party may then transmit impulses to selectivelyoperate the selector switches in the proper manner. By the employment offinder switches, each serving a relatively large number of lines, it isevident that a considerable saving may be realized in the necessaryamount of switching mechanism. But at the same time, the saving in thenumber of switches made possible by the use of line finders may only behad by sacrificing to some extent the desirable feature of immediateconnection of calling lines to idle trunks. And there is therefore, theliability of switches being improperly operated as a result of thecalling subscriber commencing to send out impulses before the finder hashad time to complete its function. With the foregoing in view thepresent invention has as its general object the provision of anautomatic telephone system, so constructed and arranged as to embody theadvantageous features of the above described methods of switchingcalling lines into connection with idle trunk circuits, and at the sametime one which practically eliminates the undesirable features of both.

Accordingly, this invention contemplates a system in which thesubscribers lines are arranged to terminate in the multiple contactbanks of finder switches, each switch serving a plurality of lines, andonly a sufli cient number of finders being allotted to each grou oflines to handle the largest number 0 simultaneous calls originating inthe group. Each line finder apportioned to a group of lines ispermanently connected by means'of a link circuit to the movable contactsof a trunk finder switch, which latter switch is operable upon theinitiation of a call in the group to which it is individual to Searchout and make connection to an idle trunk circuit leading to a firstselector switch.

Another feature consists in providing a single preselecting switch foreach of the ductors of such line are instantaneously connected, by wayof the movable contacts of the preselector switch serving such group,directly to the conductors of the particular idle first selector trunkwhich has previously been appropriated by said preselector switch.

Still another feature resides in the provision of means associated withthe preselector, and responsive to the immediate extension of aconnection therethrough to a preselected first selector trunk, to set inoperation both a line finder and trunk finder switch. The line finderthus started in motion continues to operate until it has found thecalling line, while the trunk finder continues to operate until it hasfound the particular first selector trunk to which the calling line isalready connected by way of the preselector switch. Upon theestablishment of this latter connection from a calling line to an idletrunk by means of a line finder and atrunk finder, means areautomatically operated to disable the previously mentioned connectionthrough the preselector switch, and such preselector immediatelyappropriates the next idle trunk ready for the next incoming call fromthe same line group.

Other and further features of invention will become more apparent afterhaving considered the following detailed description.

In the drawings, Figures land 2 when taken together illustrate so muchof a telephone system embodying the principles of this invention as isnecessary to a clear understanding of the manner in which connectionsare extended and completed from one subscribers line to another; andFig. 3

shows diagrammatically the manner of dividing the subscribers lines intogroups, to-

- gether with the, line finders, trunk finders,

and the preselect'ing trunk switch allotted to each oup of lines.

Re erring to the drawings and especially to Fig. 3, a generaldescription will first be given of a system involving the presentinvention, with particular reference to the division of lines intogroups, the arrangement of the finder and preselector switches in eachgroup, and the relation of the several line groups and their associatedapparatus to a group of first selector trunks. The subscribers linescomprising the entire system may be divided up into a .number of majorgroups, all the lines of such a group being common to and having accessthrough finder switches to the same group of first selector trunks. Aportion of one of these major groups is illustrated in Fig. 3 and isshown to be subdivided into minor groups, there being only three suchgroups shown, while for simplicity the several subscribers lines of eachsubgroup are designated by the single conductors 300. The incomingsubscribers lines 300 are terminated in the multiple stationary contactsof line finder switches 301. While but three lines are shown persubgroup it is evident that in practice there would be several lines,the capacity of the finders 301 being adapted to accommodate as manylines as is de- -sired to be collected in a subgroup. As will becomemore apparent hereinafter, by the novel arrangement of the presentinvention, it is possible to use single motion switches, and the finders301 preferably are constructed to operate as simple rotary switches.Although the invention is not limited to any particular capacity offinder switches it will be assumed for clearness of illustration thatthe switches 301 serve twenty-five lines, which would mean that eachsubgroup of subscribers lines 300 contain twenty-five lines, as manyfinders 301 being provided as is necessary to give the requisite gradeof service.

Each line finder 301 of a subgroup is permanently connected by a linkcircuit 302 to the movable contacts of a trunk finder switch 303. twomovable contacts per switch are diagrammatically shown in Fig. 3, thelowermost contact of each switch cooperating with a series of stationaryterminals which are each connected to a first selector trunk 304. Thesetrunk finders are of the same construction as the line finders 301,being arranged to operate as single motion rotary switches, and havingas many access points to first selector trunks as there are firstselectors allotted to a major group of subscribers lines. As anarbitrary value it is assumed that twenty-five trunks 304, each leadingto a first selector 305, will be sufiicient to serve a major group oflines comprising twelve subgroups of twenty-five subscribers lines each,three of which subgroups are shown in the drawing. Accordingly everysubscribers line 300 of any of In the trunk finders 303 but the twelvesubgroups may obtain connection through a line finder 301 and theassociated trunk finder 303 to any of the group of first selector trunks304, since the stationary terminals of the trunk finders 303 of eachsubgroup are multipled to the trunks 304.

For each subgroup of lines 300 and its associated line and trunk finderswitches there is provided a single preselecting switch 306, of the sameconstruction as the finder switches. The several lines 300 of asubgroup, as well as being terminated in the multiple terminalsof thefinders 301, are also connected to the. armatures of individual linerelays 307. The several front contacts of relays 307 of a subgroup areconnected to a common circuit 308 which leads to the movable contacts orbrushes of the preselector 306, which brushes are illustrated in Fig. 3by the lower brush of the switch 306. The stationary terminals withwhich the preselector brushes connected to the common circuit 308cotiperate, are connected as seen to the several trunks 304 in a mannercorresponding to the multiplication of the stationary terminals of thetrunk finders 303 to said trunks. The upper brush of the preselector 306corresponds to the upper brushes shown for each of the trunk finderswitches, the stationary terminals with which such brushes cooperatebeing multipled together throughout the sub roup. This multiplication ofterminals of the trunk finder switches 303 and the preselector 306within a subgroup serves, as will be more fully explained hereinafter,to control the extent of operation of a hunting finder switch 303 inaccordance with the preselection of a trunk 304 by the preselectorswitch 306. It will also be clearly brought out in the followingdescription how by the arrangement of the present invention theinitiation of a call upon any line 300 of any subgroup, such line isimmediately connected by means of its line relay 307, and thepreselector switch 306, directly to the particular first selector trunk304 that has previously been selected by said switch 306. And, moreover,it will be shown how the establishment of such a connection serves toinitiate automatically the simultaneous operation of a line finder 301and trunk finder 303, which switches remain in operation until thecalling line 300 is connected by way of the link circuit 302 to thepreselected trunk 304, whereupon the previously established temporaryconnection by way of the common circuit 308 becomes disabled.

Referring now to Figs. 1 and 2, a de tailed description will be given ofthe extension of a connection from one subscribers line to another; forwhich purpose it is assumed that the subscriber at substation 100desires to converse with the subscriber at substation 200. On theremoval of the -mary line relay. 103 individual to the line 104, 105:battery, through the upper windmg of relay 103, contact and lowerarmature of cutoff relay 106, line conductor 105, over the loop ofsubstation 100, line conductor 104, upper armature and contact of relay106 to ground. The relay 103, by energizing, establishes a circuit foritself in series with cutoff relay 106 and'a secondary line relay 107,which is likewise individual, to the calling line and corresponds to theline relays 307 shown in Fig. 3. This circuit may be followed frombattery, winding of the stepping magnet 108, armature and contact ofthis magnet, back contact and lower armature of starting relay 109,conductor 110, contact 111 of relay 107, through the winding of saidrelay 107, lower winding, contact and armature of relay 103, winding ofcutofl' relay 106, to ground. Magnet 108 is the stepping magnet for thepreselector switch brushes 112,

113, 114, 115, diagrammatically shown at 303 in Fig. 3, and is soadjusted as not to operate in series with relays 106, 103 and 107.Relays 106 and 107., however, are energized in the circuit traced, andthe relay 103 remains energized, although its initial circuit is openedby the cutoflf relay 106, with the result that the three said relays106, 103 and 107 are now all looked up over a new circuit which leadsfrom ground, winding of relay 106, armature, contact and lower windingof relay 103, through the winding, contact 111 and lower armature ofrelay. 107, to the conductor 116 common to all lines of the subgroup towhich line 104, 105 belongs, and thence to battery.

-As soon as the secondary line relay 107 attracts its armatures inresponse to the initiation of the call, the two conductors 104 and 105are connected directly to the trunk conductors 201 and 202 leading tothe first selector switch shown in Fig. 2. This circuit, which may betraced as follows, is completed through the brushes 112, 113 of'thepreselectori switch, such switch having selected the idle trunk 201, 202prior to the initiation of the call: battery, through the upper windingof first selector line relay 203, back contact and inner upper armatureof relay 204, trunk conductor 201, terminal 117 and brush 112 of thepreselector switch, conductor 118, upper middle armature and contact ofrelay 107, line conductor 104, over the loop of substation 100, lineconductor 105, upper lower armature and contact of relay 107, conductor119, brush 113, terminal 120, trunk conductor 202, lower inner armatureand back contact of relay 204, through the lower winding of relay 203,to ground. The line relay 203 energizes and the subscriber at substation100 may immediately commence to send impulses over the circuit justtraced to directively operate the first selector switch. However. itwill first be supposed that the calling subscriber does not begin tooperate his dial 121 until after suflicient time has elapsed for hisline 104, 105 to be connected to the first selector trunk 201, 202 byway of line finder brushes 122, 123. 124, 125 and trunk finder brushes126, 127,128 and 129..

' permost armature of relay 107, to ground.

Relay 109 energizes, and at itslower armature opens the circuitof-magnet 108 to prevent the same from operating due to the presence ofa ground on the terminal 131, which is applied at this time over theconductor 205 from. the upper armature and contact of relay 206. Thepresence of this ground on terminal 131 will also be trans mitted to thecorresponding terminals of preselector switches of all other subgroupsof lines, having access to the group of trunks containing trunks 201,202, since these terminals are multlipled 'throughout the severalsubgroups. ence, if apreselector in some other subgroup. happens to bestanding upon the terminal corresponding to terminal 131, or, if,inhunting for an idle trunk, comes in contact with, such terminal itwill be driven .away from this position by the completion of anoperating circuit through its stepping magnet 108.

Relay 109 at its upper armature establishes a circuit for relay 152,which results in starting in operation the first idle line finder 122,123, 124 125 and its associated trunk finder 126, 12 128, 129 of thegroup of such switches having access to the calling line. Said circuitleads from grounded battery, through the winding of relay 152, backcontact and lowermost armature of relay 132, conductor 133, right-handcontact and upper armature of starting relay 109 to ground. Relay 152completes the following circuit-for the stepping magnet 134 of the linefinder switch which interrupts its own circuit and drives the brushes122, 1 23, 124 and 125 over the terminals 135, 136, 137 and 138 of theline of the group containing the calling line; battery, contact andinner armature of relay 152, through the winding, armature and contactof magnet 134, finder test brush 125, and thence to the terminal 138,back contacts and uppermost armatures of relays 107 of all non-callinglines in the group over which the test brush 1'25 moves. Vhen, however,the brush 125 finds the ter minal 138 of the calling line, the relay 107thereof being energized as described. no ground will be present on suchterminal and consequently magnet 134 will come to rest with the finderbrushes positioned on the terminals of the calling line 104, 105.

At the same time the relay 152 at its lowerarmature establishes anoperating circuit for the stepping magnet 151, which interrupts its owncircuit and operates to drive the brushes 126, 127, 128 and 129 of thetrunk finder associated with the line finder already started inoperation, over the terminals 149,' 150, 139 and 140 of first selectortrunks in search of the particular trunk to which the calling line 104,105 is already connected by way of the preselector brushes 112 .and 113as above explained. The circuit for magnet 151 is traceable from freepole of battery, resistance 141, through the Winding of 'magnet 151,armature and contact thereof, contact and lower armature of relay 152 toground. The contacts 140 corresponding to all trunks of the group offirst selector trunks, other than the trunk .201, 202 upon thecorresponding terminal 142 of which the preselector brush 115 is nowstanding, are free from ground connections. This is true since theterminals 140 of each of the trunk finders in the subgroup are multipledto the conductor 143, which leads to the terminal 142 only of thepreselector switch individual to such subgroup, and-is not multipled topreselector switches in other subgroups. Therefore, since the brush 115can stand on but one terminal 142 at a time, and as already observedsaid brush is now positioned upon the terminal 142-which corresponds tothe selected trunk 201, 202, the trunk finder brush 129 in its movementover the terminals 140 of all other trunks will fail to find a groundconnection thereon. But when stepping magnet 151 moves the brush 129onto the terminal 140 of the preselected trunk 201, 202, the followingcircuit is established to dis continue the operation of said magnet,thereby bringing the trunk finder brushes 126, 127, 128 and 129 to restupon the proper set of terminals 149, 150, 139 and 140: battery,resistance 141, through the winding of low resistance relay 144, brush129, terminal 140, conductor 143, terminal 142, brush 115, left-handcontact and upper armature of relay 109, to ground. The resistance ofrelay 144 being low in comparison with that of magnet 151, batterycurrent is shunted around the stepping magnet in the circuit justtraced, and said magnet ceases to operate. Relay 144, however, energizesand closes a circuit from battery, contact and inner armature of ,relay152, through the winding, armature and contact of magnet 134, conductor145, lower winding of relay 132, middle armature and contact of relay144, to ground. It Wlll be observed that this circuit is in parallel tothe previously traced circuit for the line finder magnet 134 which leadsto ground at the back contact and upper armature of relay 107 of alllines encountered by the brush 125 prior to its arrival on the terminal138 'of the calling line. If then the trunk finder finds the preselectedtrunk, and the above traced circuit is completed for relay 132 beforethe line finder has completed its function, said relay does not operateby reason of a direct ground being placed upon conductor 145 at theupper armature and back contact of relays similar to relay 107. But whenthe llne finder 122, 123, 124, 125 has found the calling line, andgroundis removed from conductor 145, relay 132 receives sufficient current toenergize.

The attraction of the upper armatures of relay 132 completes theconnection from the calling line through the line finder and trunkfinder switches to the line relay 203 of the selected first selectorswitch. This circuit-may be traced from battery, through the upperwinding of relay 203, back con tact and-inner upper armature of relay204, conductor 201, terminal 149, brush 126, contact and uppermostarmature of relay 132, brush 122, terminal 135, line conductor 104, overthe loop of substation 100, line conductor 105, terminal 136, brush 123,inner upper armature and contact of relay 132, brush 127,. terminal 150,conductor 202, inner lower armature and back contact ofrelay 204, lowerwinding of relay 203, to ground. The relay 203, which is alreadyenergized over the previously described cir cuit completed at the timethe call was initiated, remains energized in this new circuit justtraced after the interruption of its first operating circuit, whichinterruption, as will presently be seen, soon takes place. \Vhen relay203 first operated, it closed a circuit for slow releasing relay 206from battery through the winding of such relay, to ground at the frontcontact and armature of relay 203. Returning to the relay 132, theenergization thereof also closes the following circuit: battery, contactand inner upper armature of slow relay 206, conductor 207, terminal 139,brush 128, contact and inner lower armature of relay 132, through theupper Winding of relay 132, brush 124, terminal 137, conductor 146,winding of relay 106, to ground. The application of battery to theconductor 146 shunts out the line relays 103 and 107,

p which up to this time have been held up in series with cutofi' relay106. Relays 103 and 107 thereupon deenergize, while the cutoff relay 106remains operated in the circuit traced to prevent the repetition of thecalling condition at the preselector switch. As soon as relay 107reacts, the temporar 1ly extended connection from the calling llne 104,105 over conductors 118 and 119 to the trunk 201, 202 is opened, and theline is now connected through to the selector only by way of the finderswitches. The upper armature of relay 107 in retracting opens at itsfirst front contact the circuit of starting relay 109, and at its backcontact places a ground upon terminal 138 of other line finders of thegroup to render the line 104, 105 non-calling. The presence of a groundon terminal 138 of the operated finder does not cause any furthermovement thereof at this time since the circuit of magnet 134 hasalready been opened by relay 152, which relay deenergized upon theoperation of relay 132. The retraction of the arinatures of relay 109closes the fol lowing circuit for the stepping magnet 108 of thepreselector switch 112, 113, 114, 115: battery, through the winding ofsuch mag- .net armature and contact thereof, back contact and lowerarmature of relay 109, brush 114, terminal 131, conductor 205, uppermostarmature and contact of relay 206 to ground. Stepping magnet 108'operates and steps the brushes 112, 113, 114 and 115 of the preselectoronto the, terminals of the next first selector trunk in the group. Ifsuch trunk happens to be busy there will be a ground on terminal 131corresponding thereto, and the preselector is moved over a second step.-This operation continues until an idle trunk is located, whereupon thepreselector'is arrested and awaits in readiness for the next call of itsindividual subgroup of lines. Upon the initiation of a second call onanother line in the same subgroup of lines, the secondary line relay,

lay 109, conductor 133, lowermost armature and front contact of relay109, conductor 133, lowermost armature and front contact of relay 132,inner armature and contact of relay 144, now denergized, outstarter wire148, to the next idle line finder and its associated trunk finder switchin the group.

The calling line 104, 105 having thus been extended through to the firstselector switch, the calling subscriber, who as originally assumed doesnot begin to send out impulses until the finder switches have had timeto find his line, now manipulates the dial 121 to directively operatethe first selector switch in accordance 'with the first digit of thecalled number. For each interruption of the line by the sender 121 theline relay 203 retracts its armature. At the first retraction of thearmature of said relay the following circuit is closed: groundedarmature and back contact of relay 203, lowermost armature of relay 204,lower armature and front contact of slow relay 206, through the windingof relay 208, winding of primary stepping magnet 209, to battery. Theprimary magnet 209 operates and steps the first selector brushes 210,211and 212 up one step into operative relation to the first level oftrunks. For each succeeding retraction of the armature of relay 203magnet 209 advances the brushes 210, 211 and 212 one step, and finallyat the termination of the series of impulses brin s them to restopposite the desired level of trunk terminals. On the f,

:st vertical step of the brush shaft (not s'h"'wn) the primary ofinormalcontact 213 is closed. Relays 208 and 206 being slow to releaseholdtheir armatures attracted during/the operation of magnet 209 with theresult that the following circuit is established as soon as theolf-normal contact 213 is closed: free pole of battery, through thewinding of relay 214, off-normal contact 213; front contact and armatureof relay 208; upper armature and contact of relay 206 to ground. Relay214 energizes in this circuit and closes another circuit for itselfindependent of the contact of relay 208, which may be traced frombattery, winding of relay 214, off-normalcontact 213, conductor 215,armature and contact of the secondary stepping magnet 216, to ground atthe upper armature and contact of relay 214.

At the end of the primary series of impulses, and after rela 203 remainsenergized for a suflicient perio relay 208 releases its armature toclose a circult from battery, through winding of secondary magnet 216,

inner armature and contact of relay 214,

back contact and armature of relay 208, to

' ground at the upper armature and contact of relay 206. The magnet 216energizes in this circuit and operates in the wellknown manner to rotatebrushes 210, 211, 212 into en agement with the first set of terminals 21218, 219 in the selected level. Magnet 216 by attracting its armaturealso opens the above traced circuit for relay 214, causing said relay tobecome .deenergized. Relay 214' on .retracting its armatures in turnopens the circuit of the magnet 216, which thereupon deenergizes,preparatory to giving the brushes 210, 211, 213 a second step forward.If the first trunk in the group is busy this condition will bemanifested by the presence of a ground upon the test terminal 219thereof. As soon, there-' fore, as the magnet 216 deenergizes afterhaving imparted its first step to the brushes 217, 218, 219, a circuitis closed as follows to again energize the relay 214: battery, windingof relay 214, contact 213, conductor 215, armature and contact of magnet216,

conductor 220, back contact and upper armature of relay 204, conductor221, brush 212,

ceeds, the relay 214 being successively energized at the end of eachstep by ground connections on the test terminals of busy trunks, untilbrushes 210, 211, 212 arrive upon the terminals 217, 218, 219 of an idletrunk leading to the next switch.

It is to be noted that while the switch is in its secondary movementeach time a circuit is completed. for relay 214 a parallel circuit isalso\established including relays 214 and 204 in series. ablefrom'battery, winding of relay 214, contact 213, conductor 215, armatureand contact of magnet 216, conductor 220, winding of relay 204, toground at the up er armature and contact of relay 206. wever, during thehunting operation of th'%itch the relay 214 is energlzed by a circuitich leads, as above described, directly to he grounded test wire 221,and the relay 204 ing shunted thereby does not actuate at th s time. Butas soon as the hunting movemen is completed brush 212 stands ona, non lgrounded terminal 219, and relays 214' and\100 This circuit is trace- 7204 are connected in series with each other in the circuit .just traced.-Relays 214 and 204 are so constructed that when laced in series witheach other relay 204 receives sufficient current to operate, while relay214 remains inert. The attraction of the armatures of relay 204disconnects the trunk conductors 201 and 202 from the selector line cuitfor relay 204 until the connector line I relay (not shown) has had timeto operate and place a ground back upon the test wire 221 inawell-lgnownmanner. With a ground on wire 221' the relay 204 is heldenergized from battery, through the winding of relay- 214, contact 213,conductor 215, armature and contact of magnet 216, conductor 220,

winding of relay 204, front contact and uppermost armature of relay 204,to the grounded test Wire 221. The ground conneetion applied toconductor 221 from the connector switch is also transmitted by way ofthe uppermost armature and front contact of relay 204 and conductor 205to the multiple terminals 131 of all preselector switches to substitutefor the ground at the ll hen slow relay 206 deenergizes, it removesbattery from conductor 207 at its inner upper armature, but relays 132and 106 are maintained energized by the application of battery currentto conductor 207 at the primary off-normal contact 227.

The calling subscriber may now operate his dial 121 to transmit the tensand units series of impulses, which are effective to step the connectorbrushes 224, 225, 226 into en-. gagement with the terminals 228, 229,230 of the called line 200.

At the termination of conversation when the subscribers have replacedtheir receivers on switchhook, the connector restores and removes groundfrom the test wire 221. Removal of ground from said testwire causes thedeenergization of relay 204, which completes the following circuit forthe selector release magnet 231: battery, winding of magnet 231, primaryofi-normal contact 232, back contact and lower armature of relay 206,lower armature and contact of relay 204, back contact and armature ofrelay 203, to ground. After the selector switch is completely restoredby release magnet 231, the primary off-normal contact 227 is openedto'remove battery from conductor 207. Relays 132 and 106 thereuponrelease, the former of which opens the link circuit between the linefinder and trunk finder used in extending the call, and also connectsthe starter WlI' 133 to the relay 152. while the cutoff relay 106 placesthe line 10-1, 105 in its normal condition. Ground is also removed Ifrom conductor 205 so that the first selector trunk 201, 202 againbecomes available to the preselector switch 112, 113, 114, 115 of anysubgroup of lines. All apparatus involved in the extension of theconnection is now in its idle condition and may again be taken for use.The line finder 122,123, 124:, 125 and trunk finder 126, 127, 128, 129,which as explained are simple rotary switches,'do not return to a normalposition at the end of each call but remain in the position last usedready to be operated when the next call comes in.

From the above description of the novel arrangementv employed forautomatically switching calling lines into connection with idle trunks,it is obvious that the calling subscriber after having initiated thecall may immediately begin to send out impulses to operate a firstselector switch. Assume then that the subscriber at substation 100,after having removed his receiver from the hook, commences at once tomanipulate the dial 121. As was previously explained the removal of thereceiver from the hook causes the energization of secondary line relay107,

pper armature and contact of relay 206.

which connects the line 104, 105 directly to the preselected idle trunk201, 202 by way of the preselector brushes 112 and 113. Operation of thedial 121 therefore causes the selector line relay 203 to vibrate in theusual manner to actuate the brushes 210, 211, 212 to the proper group oftrunks. In the meantime the line finder 122, 123, 12 1. 125 and trunkfinder 126, 127, 128, 129 are started in operation, as has been clearlyexplained, and continue their hunting movement until the calling line104, 105 is connected by way of these switches to the selected trunk201, 202. In case the finder switches should complete their operationduring the time the subscriber is sending impulsesato the first selectorby way of the preselector switch there is no liability of mutilatingsuch impulses since the temporarily established circuit through thepreselector is not interrupted until after the permanent connection tothe first selector trunk is completed by the finder switches. X

What is claimed is:

1. In a telephone system, a telephone line, a trunk circuit, relaysresponsive to the initiation of a call on said line for establishing aconnection between said line and trunk circuit, and means alsoresponsive to the initiatlon of said call for establishing a secondconnection between said line and trunk circuit.

2. In a telephone system, a line, a trunk circuit, a relay forconnecting said line to said trunk circuit, and means operated upon thecompletion of such connection for establishing a second connectionbetween said line and trunk circuit.

3. In a telephone system, a telephone line,

a trunk circuit, relays for establishing a connection between said lineand trunk circuit, means operated upon the completion of such connectionfor establishing a second connection between said line and trunkcircuit, and means operated upon the completion of said secondconnection for disestablishin said first connection.

4. 1% a telephone system, a telephone line,

a primary and a secondary line relay therefor, a trunk circuit, meansresponsive to the initiation of a call on said line for establishing aplurality of separate connections between said line and trunk circuit,one of said connections being immediately established upon theenergization of said line relays, and means operated when all of saidconnections have been completed for disestablishing one of saidconnections.

5. In a telephone system, a line, a trunk circuit, relays responsive tothe initiation A trunk circuit, means operated upon the comtiation ofsaid call for starting the operation of said switches.

6. In a telephone system, a line, a trunk circuit, means forestablishing a connection between said line and trunk circuit, automaticswitches for establishing a second conpletionof said first connectionfor starting the operation of said switches, and means operated upon thecompletion of the movement of said switches for disestablishing saidfirst connection.

- In a telephone system,'a telephone line. trunk circuit, meansoperative to establ sh a connection between said line and trunk circuit,a plurality of automatic switches for establishing a second connectionbetween said line and trunk circuit, and means operated upon theestablishment of said first connection for starting simultaneously theoperation of said automatic switches.

' 9. In a telephone system, a telephone line,

a trunk circuit, means operative to establish a connection between saidline and trunk circuit, a plurality of automatic switches forestablishing a second connection between. said line and-trunk circuit,means operated upon the establishment of said first connection forstarting simultaneously the operation of said automatic switches, andmeans operated when all of said switches have completed their movementto disestablish said first connection. f

10. In a telephone system, a telephone line,

' a trunk circuit, relays responsive to the initiation of a call on saidline for establishing a connection between said line and trunk circuit,an automatic switch also responsive to the initiation of said call forestablishing a second connection between said line and trunk circuit,and means operated when said switch has completed its movement todisestablish said first connection.

11. In a telephone system, a line, a trunk circuit, link circuits forinterconnecting said inc and trunk circuit, means responsive to theinitiation of a call upon said line for immediately effecting aconnection between said line and trunk circuit over one of said linkcircuits, a finder switch, and means also responsive to the initiationof said call for operating said finder ,to connect said line to saidtrunk circuit over another of said link circuits.

12. In a telephone system, a line, a trunk circuit, link circuits forinterconnecting said immediately eifecting a means responsive to uponsaid line for connection between said line and trunk circuit over one ofsaid link circuits, finder switches, and means operated upon theestablishment of said connection for starting one of said switches inoperation to find said line and for starting another-of said switches inoperation to find said trunk circuit to establish a second conline andtrunk circuit, the initiation of a call nection between said line andtrunk circuit over another of said link circuits.

13. In a telephone system, a line, a trunk circuit, link circuits forinterconnecting said line and trunk circuit, means responsive to theinitiation of a call on said line for immediately establishing aconnection between said line and trunk circuit ,over one of sald linkcirciiits, means also responsive to the initiation of such call forestablishing a second connection between said line and trunk circuitover another of said link circuits, and ase'nder associated with thecall ing line for transmitting impulses to said trunk over either-ofsaid link circuits.

14. In a telephone system, a line, a trunk circuit, link circuits forinterconnecting said line and trunk circuit, relays responsive to theinitiation of a call on said line for establishing a connection betweensaid line and trunk circuit over one of' 'said link circuits, meansoperated upon the completion of such connection for establishing asecond connection between said line and trunk circult over another ofsaid link circuits, means operated upon the completion of such secondconnection for disestablishing said first connection, with said line forsending impulses to said trunk over either of said link circuits.

15. In a telephone system, a line, a trunk terminating in a selectiveswitch, link circuitsfor interconnecting said line and trunk, relaysresponsive to the initiation of a call on said line forestablishing aconnection between said line and trunk over one of said link circuits,finder switches, means operated upon the completion of said connectionfor starting the finder switchesin operation to establish a secondconnection between said line and trunk over a second one of said linkcircuits, and acalling device associated with the calling line forsending impulses over said first link circuit to .the selective switchwhile said finder switches are in operation and for sending impulsesover said second link circuit to the selective switch after the findershave completed their operation.

16. In a telephone system, a plurality of lines, a plurality of trunks,link circuits for interconnecting said lines and trunks, means operatedin response to .the initiation of a call on one of said lines to connectsuch line to an idle one of said trunks over one of said link circuits,finder switches, means operand a calling device associated ated inresponse to the initiation of said call for starting one of said findersin operation to find the calling line and for starting another finder inoperation to find said idle trunk, to establish a second connectionbetween said line and idle trunk over another of said link circuits, andmeans for preselecting idle trunks.

17. In a telephone system, a plurality of lines, a group of trunks, linkcircuits for interconnecting said lines and trunks, means operative toconnect a calling line to an idle one of said trunks over one of saidlink circuits, finder switches, means controlled in the establishment ofsaid connection for starting one of said switches in operation to findthe calling line and for starting another of the switches in operationto find said idle trunk, to establish a second connection between saidline and idle trunk over another of said link circuits, means controlledin the establishment of the connection over said second link circuit fordisestablishing the connection over said first link circuit, and meansfor preselecting idle trunks in said group.

18. In a telephone system, a plurality of lines, a group of trunks, apreselector switch for preselecting idle trunks in said group, a

ing line and for starting said trunk finder selector switch to preselectthe next idle trunk in the group.

19. In a telephone system, a plurality of groups of lines, a group oftrunks for serving said lines, a connecting circuit for each group oflines including a preselector switch arranged to preselect idle trunksin said group, a plurality of link circuits for each group of lines eachincluding a line finder and a trunk finder, means operated upon theinitiation of a call on any line in any group for connecting said lineto a preselected idle trunk over the connecting circuit individual tosuch group of lines, means controlled in the establishment of suchconnection for starting the operation or the line finder and trunkfinder included in an idle link circuit individual to the groupcontaining the calling line, said line finder operating to find thecalling line and said trunk finder operating to find said preselectedtrunk to thereby connect said calling line to the preselected trunk oversaid idle link circuit, means operated to thereupon disestablish theconnection over said connecting circuit and to operate the preselectorswitch to preselect the next idle trunk in the group.

In witness whereof, I hereunto subscribe my name this 25th day of MarchA. D., 1918.

WINFRED '1. POWELL.

